So personally I purged all of my denim minis (actually all of my denim skirts, period, but that is a different story) a couple of seasons ago because I was never wearing them precisely because they felt too young. I have issues with that though - I look really young and am always getting mistaken for a student even though I am 32, so I try not to dress that way too. Anyway, the minis were getting to feel too short for comfort anyway, and with leggings I think they looked even more young.
Just my take though.. and Mo is right, if you live somewhere beachy or casual (unlike me, who lives in a urban environment and works somewhere full of students), it's probably a much more all-ages vibe.